CDMA/TDMA spread-spectrum communications system and method

ABSTRACT

A spread-spectrum transmitter and receiver using code division multiple access with time division multiple access technology for spread-spectrum communications. At a base station, a spread-spectrum transmitter includes a multiplexer for time multiplexing a synchronization-code signal and a plurality of data signals, which may be encoded as a plurality-encoded data signals, to generate a time-multiplexed signal. A chip-code generator generates a chip-code signal which is modulo added with the time-multiplexed signal by an EXCLUSIVE-OR gate to generate a spread-spectrum-time-multiplexed signal. A transmitter transmits the spread-spectrum-time-multiplexed signal over a communications channel. A spread-spectrum receiver at the base station processes a plurality of spread-spectrum signals, received from a plurality of remote units in as time division sequence of spread-spectrum signals, using a despreader circuit to generate a time-division signal. A demultiplexer demultiplexes the time-division signal as a plurality of data signals or as a plurality of privacy-encoded data signals. A remote unit, which may be a handset, includes a despreader circuit for despreading the spread-spectrum-time-multiplexed signal as a time-multiplexed signal. A synchronization-code matched filter detects the synchronization-code signal embedded in the time-multiplexed signal and thereby generates a timing signal. A controller uses the timing signal to generate a control signal. The control signal controls a transmit-receive switch for switching an antenna between the despreader circuit to the transmitter at the remote unit.

BACKGROUND OF THE INVENTION

The present invention relates to spread-spectrum communications, andmore particularly to a direct sequence, code division multiple access,time division multiple access, spread-spectrum system.

DESCRIPTION OF THE RELEVANT ART

Spread-spectrum modulation has been, and still is used extensively inmilitary communications systems both to permit communications which arenot detectable by enemy jamming systems, and to resist jamming by anenemy desiring to disrupt communications. Signals which are notdetectable by enemy intercept systems are called low probability ofintercept signals.

For commercial applications using spread-spectrum modulation, fullduplex operation is desirable, allowing a base station and a remote unitto communicate with each other simultaneously. One approach for fullduplex is to assign a pair of chip codewords unique to the base stationand the remote unit, and have them communicate simultaneously in timeand at the same carrier frequency with each other. A problem with thisapproach is that the spread-spectrum signal radiated at the remote unitraises the noise level at the input to the spread-spectrum receiver atthe remote unit.

Another approach for full duplex operation, which alleviates the problemof having the spread-spectrum transmitter raising the noise power levelat the input to the spread-spectrum receiver at the remote unit or basestation, is to assign different carrier frequencies for transmitting andreceiving. Thus, the base station may communicate to a plurality ofremote units at a first carrier frequency f₁ and the plurality of remoteunits may communicate to the base station at a second carrier frequencyf₂. Using two carrier frequencies requires filters at each remote unitand at the base station to prevent leakage of signal energy from therespective spread-spectrum transmitter to the spread-spectrum receiverat each remote unit and at the base station. Additionally, different andlong chip codewords are required with multiple remote units, whichrequire complicated acquisition and tracking circuits. Using filters andlong chip codewords adds to increased circuit complexity and cost.

OBJECTS OF THE INVENTION

A general object of the invention is a mobile cellular communicationssystem, which allows full duplex operation without the need for complexfilters for separating transmitter and receiver frequencies and complextracking and acquisition circuits.

Another object of the invention is an inexpensive personalcommunications network, mobile cellular communications system.

An additional object of the invention is a spread-spectrumcommunications system which has little or no interference between users.

A still further object of the invention is a spread-spectrum system inwhich the system performance is thermal noise power limited rather thaninterference limited.

SUMMARY OF THE INVENTION

The present invention provides a system and method which transmit a codedivision multiple access (CDMA), time division multiple access (TDMA),spread-spectrum communications signal between a base station and aplurality of remote units. The base station time multiplexes asynchronization-code signal and a first plurality of data signals, or afirst plurality of privacy-encoded data signals, to generate atime-multiplexed signal, and then spread-spectrum processes thetime-multiplexed signal with a first chip-code signal to generate aspread-spectrum-time-multiplexed signal. Thespread-spectrum-time-multiplexed signal is defined herein to include atime-multiplexed signal which is spread-spectrum processed with achip-code signal.

Each remote unit receives and despreads thespread-spectrum-time-multiplexed signal, and demultiplexes a respectivedata signal being sent to the remote unit embedded in thetime-multiplexed signal as a function of the synchronization-codesignal. At a specified time, the remote unit sends a remote-data signal,or a remote-privacy-encoded data signal, to the base station byspread-spectrum processing the remote-data signal, orremote-privacy-encoded data signal, and transmitting the spread-spectrumsignal over the communications channel. Since the remote unit is nottransmitting and receiving at the same time, a transmit-receive switchcan be employed to switch an antenna between the despreader circuitryand the transmitter at the remote unit. A remote-data signal is definedherein as a data signal being sent from a remote unit to the basestation. A remote-privacy-encoded-data signal is defined herein as anencoded remote-data signal being sent from the remote unit to the basestation.

At the base station, a plurality of spread-spectrum signals are receivedfrom the plurality of remote units as a spread-spectrum-time-divisionsignal, which is despread as a time-division signal. The time-divisionsignal accordingly is demultiplexed as a plurality of remote-datasignals, or a plurality of remote-privacy-encoded data signals. Thespread-spectrum-time-division signal is defined herein to include aplurality of spread-spectrum signals received sequentially in time froma plurality of remote units. The time-division signal is defined hereinto include a plurality of remote-data signals, or a plurality ofremote-privacy-encoded data signals, which are in different time slotsdue to the timing of when they are sent from each of the plurality ofremote units.

More particularly, a spread-spectrum transmitter at the base stationincludes base-synchronization means, a plurality of base-privacy means,multiplexer means, base-spreading means, and base-transmitter means. Thesynchronization means generates a synchronization-code signal, and theplurality of base-privacy means encodes a plurality of data signals witha plurality of privacy-code signals as a plurality of privacy-encodeddata signals, respectively. The encoding with a privacy-code signal maybe an encryption type of privacy, or a less secure type of privacy. Themultiplexer means time multiplexes the synchronization-code signal andthe plurality of privacy-encoded data signals, respectively, to generatea time-multiplexed signal. The base-spreading means spread-spectrumprocesses the time-multiplexed signal with a first chip-code signal togenerate a spread-spectrum-time-multiplexed signal. The time-multiplexedsignal is converted by base-transmitter means to a form suitable forsending over the communications channel.

The plurality of base-privacy means is optional, and accordingly, theplurality of data signals need not be encoded with the plurality ofprivacy-code signals as a plurality of privacy-encoded data signals. Ifthe plurality of privacy means were not used, then the multiplexer meanstime multiplexes the plurality of data signals to generate atime-multiplexed signal.

The spread-spectrum receiver at the base station processes aspread-spectrum-time-division signal using base-despreader means,base-demultiplexer means, base-synchronization means, and optionally, aplurality of base-decoder means. The base-despreader means despreads areceived spread-spectrum-time-division signal as a time-division signal.The base-demultiplexer means demultiplexes the time-division signal as aplurality of remote-data signals or, in the event the plurality of datasignals were encoded, as a plurality of remote-privacy-encoded datasignals. The base-synchronization means, which is the same as used by,and operates cooperatively with, the spread-spectrum transmitter at thebase station, generates the synchronization-code signal and a timingsignal. In response to the timing signal, each of the base-decoder meansdecodes each of the remote-privacy-encoded signals as a remote-datasignals.

At a remote unit, a spread-spectrum-time-multiplexed signal is receivedat the first carrier frequency. As set forth previously, thespread-spectrum-time-multiplexed signal includes a synchronization-codesignal and a plurality of privacy-encoded data signals. Theprivacy-encoded-data signal to be received by the remote unit is definedherein to be the first privacy-encoded-data signal. A remote-data signalis spread-spectrum transmitted from the remote unit at a second carrierfrequency.

The remote unit includes remote-despreader means, remote-synchronizationmeans, control means, remote-decoder means, remote-privacy means,remote-spreading means, and remote-transmitter means. Theremote-despreader means despreads the spread-spectrum-time-multiplexedsignal received from the base station as a time-multiplexed signal. Theremote-synchronization means detects the synchronization-code signalembedded in the time-multiplexed signal, and generates a timing signal.The control means generates a control signal in response to thesynchronization-code signal. The control signal has the proper timing,relative to the synchronization-code signal, for operating the remoteunit. The proper timing includes having the appropriate data signal orprivacy-encoded data signal embedded in the time-multiplexed signalstored in a buffer. The remote-decoder means, using timing from thecontrol signal, decodes a first privacy-encoded data signal embedded inthe time-multiplexed signal as a first data signal.

In response to the control signal, the remote-privacy means encodes theremote-data signal with a remote-privacy-code signal as aremote-privacy-encoded data signal. The remote-privacy-code signal isdefined herein to include any signal that can be used to encrypt or addprivacy to the remote-data signal. The remote-spreading meansspread-spectrum processes the remote-privacy-encoded data signal with asecond chip-code signal as a spread-spectrum signal. Theremote-transmitter means at the remote unit converts the spread-spectrumsignal to a form suitable for sending over the communications channel.The second chip-code signal, which is generated at each of the pluralityof remote units, may be the same as the first chip-code signal generatedat the base station.

The present invention also includes, at a base station, the method forspread-spectrum processing a plurality of data signals on a firstcarrier frequency by generating a synchronization-code signal, encodingthe plurality of data signals with a plurality of privacy-code signalsas a plurality of privacy-encoded data signals, time multiplexing thesynchronization-code signal and the plurality of privacy-encoded datasignals, respectively, to generate a time-multiplexed signal,spread-spectrum processing the time-multiplexed signal with a firstchip-code signal to generate a spread-spectrum-time-multiplexed signal,and converting the spread-spectrum-time-multiplexed signal to a formsuitable for sending over the communications channel.

Also, at the base station, the method includes receiving aspread-spectrum-time-division signal by despreading thespread-spectrum-time-division signal as a time-division signal,demultiplexing the time-division signal as a plurality ofremote-privacy-encoded data signals, generating a timing signal, anddecoding, using the timing signal, the plurality ofremote-privacy-encoded signals as a plurality of remote-data signals.

Additional objects and advantages of the invention are set forth in partin the description which follows, and in part are obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention also may be realized and obtained bymeans of the instrumentalities and combinations particularly pointed outin the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate particular embodiments of theinvention, and together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a block diagram of a base station transmitter;

FIG. 2 is a block diagram of a base station receiver;

FIG. 3 is a block diagram of a remote unit transmitter and receiver;

FIG. 4 is a block diagram of a correlator for despreadingspread-spectrum signals;

FIG. 5 is a timing diagram of multiplexed data from the base station ofFIGS. 1 and 2;

FIG. 6 is a timing diagram of a packet of data transmitted from a firstremote unit relative to the multiplexed data transmitted from the basestation of FIGS. 1 and 2;

FIG. 7 is a block diagram of a base station transmitter;

FIB. 8 is a timing diagram of data transmitted between the base stationof FIG. 7 and a plurality of remote units;

FIG. 9 is a block diagram of a base station transmitter; and

FIG. 10 is a timing diagram of data transmitted between the base stationof FIG. 9 and a plurality of remote units.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to the preferred embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals indicate to like elementsthroughout the several views.

In the exemplary arrangement shown in FIG. 1, a spread-spectrumtransmitter which can be used for spread-spectrum processing a pluralityof data signals on a first carrier frequency f₁, is shown comprisingbase-synchronization means, a plurality of base-privacy means,multiplexer means, base-spreading means, and base-transmitter means. Thebase-synchronization means is coupled to the multiplexer means. Theplurality of base-privacy means is coupled between a plurality of inputshaving the plurality of data signals, and the multiplexer means. Theplurality of data signals includes the first data signal, d₁ (t), seconddata signal d₂ (t), through N^(th) data signal, d_(N) (t). Each datasignal is assumed to be sent to a respective remote unit. Thebase-spreading means is coupled between the multiplexer means and thebase-transmitter means.

The base-synchronization means is shown as a synchronization codegenerator 81 and the synchronization buffer 82. The synchronizationbuffer 82 is coupled to the synchronization code generator 81. Alsoshown is a clock 57 which is coupled through a first divider 55 and asecond divider 54 to the synchronization-code generator 81.

The plurality of base-privacy means is embodied as a plurality ofprivacy-code generators, shown as first privacy-code generator 52,second privacy-code generator 62, through N^(th) privacy-code generator72, coupled to a plurality of EXCLUSIVE-OR gates, shown as firstEXCLUSIVE-OR gate 51, second EXCLUSIVE-OR gate 61, through N^(th)EXCLUSIVE-OR gate 71, respectively. More particularly, the firstEXCLUSIVE-OR gate 51 is coupled to the first privacy-code generator 52and to a first input having the first input signal, d₁ (t) The secondEXCLUSIVE-OR gate is coupled to the second input which provides thesecond data signal, d₂ (t), and to second privacy-code generator 62. TheN^(th) EXCLUSIVE-OR gate is coupled to the N^(th) input which providesthe N^(th) data signal, d_(N) (t), and to the N^(th) privacy-codegenerator 72.

The multiplexer means is embodied as a plurality of buffers, shown asfirst buffer 53, second buffer 63 through N^(th) buffer 73 and asynchronization buffer 82, and a multiplexer 75. The multiplexer 75 iscoupled to the first buffer 53, second buffer 63, through N^(th) buffer73, and to the synchronization buffer 82. The first buffer 53 is coupledto the first EXCLUSIVE-OR gate 51. The second buffer 63 is coupled tothe second EXCLUSIVE-OR gate 61. The N^(th) buffer 73 is coupled to theN^(th) EXCLUSIVE-OR gate 71. The synchronization buffer 82 is coupled tothe synchronization-code generator 81. The multiplexer 75 has its timingcoupled to the output of the first divider 55. The first divider 55divides the time of the clock signal from clock 57.

The base-spreading means is embodied as an EXCLUSIVE-OR gate 76, lowpassfilter 77, and a chip-code generator 56. The EXCLUSIVE-OR gate 76 iscoupled to the multiplexer 75, to the lowpass filter 77, and to thechip-code generator 56. The chip-code generator 56 also is coupled tothe clock 57. The output of the EXCLUSIVE-OR gate 76 is coupled to alowpass filter 77.

The clock 57 provides a appropriate clock signal for operation of thespread-spectrum transmitter and receiver at the base station. The clocksignals are time divided by first divider 55 and second divider 54. Thedivided clock signal outputted from second divider 54 is used for timingof the plurality of privacy-code generators, and the synchronizationcode generator. The divided clock signal outputted from first divider 55is used for timing of the multiplexer 75. For the embodiment of FIG. 1,the first divider 55 divides the timing of the clock signal by 15, andthe second divider 54 divides the timing from the first divider 55 by100.

The base-transmitter means is embodied as an oscillator 74 whichgenerates a first carrier frequency, f₁, a product device 78, and apower amplifier 79. The product device 78 is coupled between theoscillator 74, and the lowpass filter 77 and power amplifier 79. Theoutput of the power amplifier 79 typically is coupled through anisolator 99 which may be embodied as a circulator, to an antenna 98. Theisolator 99 also is coupled to a receiver at the base station.

The plurality of data signals, d₁ (t), d₂ (t), . . . , d_(N) (t), areencoded by the plurality of EXCLUSIVE-OR gates 51, 61, 71 with theplurality of privacy-code signals, g₁ (t), g₂ (t), . . . , g_(N) (t),which are generated by the plurality of privacy-code generators 52, 62,72, respectively. The plurality of EXCLUSIVE-OR gates 51, 61, 71modulo-2 add each of the respective privacy-code signals g₁ (t), g₂ (t),. . . , g_(N) (t), to each of the plurality of data signals, d₁ (t), d₂(t), . . . , d_(N) (t), respectively, to generate a plurality ofprivacy-encoded-data signals. The plurality of privacy-encoded-datasignals are stored in the plurality of buffers 53, 63, 73.

Each of the privacy-code signals may be an encrypting signal or a signalwhich provides privacy to particular data signal, as is well known inthe art. Other types of encoding may be used, such as encryption withthe Data Encryption Standard.

The synchronization-code generator 81 generates a synchronization-codesignal. The synchronization-code signal is stored in the synchronizationbuffer 82.

The multiplexer 75 from the synchronization buffer 82 time multiplexesthe synchronization-code signal and from the plurality of buffers 53,63, 73, the plurality of privacy-encoded-data signals, respectively, togenerate a time-multiplexed signal. Typically, the synchronization-codesignal is initially time multiplexed in a first time slot, and thensequentially, the first privacy-encoded-data signal, secondprivacy-encoded-data signal, through N^(th) privacy-encoded-data signalare time multiplexed in subsequent time slots. A frame of data isdefined herein as the time-multiplexed synchronization-code signal andthe plurality of privacy-encoded signals. Accordingly, atime-multiplexed signal includes a frame of data. Thesynchronization-code signal may be a sequence of 1-bits and 0-bits usedfor identifying the beginning of each frame of data.

Based on the timing from the synchronization-code signal, a particularprivacy-encode data signal can be determined. Preferably, each of theprivacy-encoded-data signals and the synchronization-code signal havethe same number of bits for a time slot, although a different lengthsequence of bits could be used for the synchronization-code signal.

The chip-code generator 56 generates a first chip-code signal using afirst chip codeword. The time-multiplexed signal outputted from themultiplexer 75, and the first chip-code signal, C_(B) (t), from thechip-code generator 56, are spread-spectrum processed by theEXCLUSIVE-OR gate 76 to generate a spread-spectrum-time-multiplexedsignal. The spread-spectrum processing typically is modulo-2 adding thetime-multiplexed signal with the chip-code signal using the EXCLUSIVE-ORgate 76. The lowpass filter 77 filters thespread-spectrum-time-multiplexed signal to remove out-of-band energy.The filtered spread-spectrum-time-multiplexed signal is then frequencytranslated, by operation of the product device 78 and the first carriersignal supplied by the first oscillator 74, to the first carrierfrequency, f₁. Thus, after amplification by power amplifier 79, thespread-spectrum-time-multiplexed signal is transmitted at the firstcarrier frequency, f₁, by antenna 98 over a communications channel.

As an example, assume the synchronization-code signal and 100privacy-encoded data signals are multiplexed by the multiplexer 75 atmultiplex rate, f_(M). In this example, assume that each data signal issampled at the rate of 16 kilobit per second (kb/s) and compressed bythe factor 101. The resulting data rate, d_(M), in the time-multiplexedsignal is 101×16 kb/s, which is approximately 1.6 Mb/s. Thetime-multiplexed signal is then spread by EXCLUSIVE-OR gate 76 using ashort first chip-code signal generated from a 15 chip codeword bychip-code generator 56. Each remote unit uses the same first chip-codesignal, C_(B) (t).

As illustratively shown in FIG. 2, a spread-spectrum receiver forspread-spectrum processing a spread-spectrum-time-division signal isshown comprising the antenna 98, the isolator 99, a bandpass filter 101,a low noise amplifier (LNA) 102, a mixer 103, local oscillator 104,automatic-gain-control (AGC) circuit 105, base-despreader means,base-demultiplexer means, base-synchronization means, and base-decodermeans. The bandpass filter 101 is coupled through the oscillator 99 tothe antenna 98. The isolator 99 also coupled to the transmitter ofFIG. 1. The low noise amplifier 102 is coupled between the mixer 103 andthe bandpass filter 101, and the mixer 103 is coupled to the localoscillator 104 which generates a first local signal. The AGC circuit 105is coupled between the mixer 103 and the base-despreader means. Thebase-demultiplexer means is coupled to the base-despreader means, to thebase-synchronization means and to the base-decoder means.

In FIG. 2, the base-despreader means is embodied as despreader circuitry110, the base-demultiplexer means is embodied as the demultiplexer 115,the base-synchronization means is embodied as the synchronization-codegenerator 81 and the timing and synchronization circuit 120, and thebase-decoder means is embodied as a privacy-code generator 121 and anEXCLUSIVE-OR gate 122. The despreader circuitry 110 may be a matchedfilter, a correlator, or any other circuit which can be used fordespreading a received spread-spectrum signal having spread-spectrummodulation. A matched filter may be implemented using atapped-delay-line filter, such as a surface-acoustic-wave device. Atypical correlator which can be used for despreading a spread-spectrumsignal is depicted in FIG. 4, and includes a mixer 410, chip-codegenerator 415 and filter 420.

The demultiplexer 115 is coupled to the despreader circuitry 110. Thesynchronization-code generator 81 is coupled to the timing andsynchronization circuit 120, and the timing and synchronization circuit120 is coupled to the demultiplexer 115 and to the privacy-codegenerator 121. The privacy-code generator is coupled to the EXCLUSIVE-ORgate 122. For this particular embodiment, the base-decoder means, andaccordingly the privacy-code generator 121, are shown for decoding aparticular remote privacy-encoded data signal from the plurality ofremote-privacy-encoded data signals received by the spread-spectrumreceiver. Normally, a plurality of base-decoder means would be employedfor decoding a plurality of remote-privacy-encoded-data signals.

A spread-spectrum-time-division signal received by antenna 98 passedthrough oscillator 99 and is filtered by bandpass filter 101 andamplified by low noise amplifier 102. The mixer 103, using the firstlocal signal from the local oscillator 104, shifts the receivedspread-spectrum-time-division signal to the appropriate intermediatefrequency or to baseband frequency for processing by the despreadercircuitry 110. The appropriate frequency depends on the particularembodiment of the despreader circuitry 110. The AGC circuit 105normalizes the power of the received spread-spectrum-time-divisionsignal.

The spread-spectrum-time-division signal is defined herein to include aplurality of spread-spectrum signals received sequentially in time fromthe plurality of remote units. Each remote unit transmits aspread-spectrum signal for a short duration in time. The timing fortransmitting from a particular remote unit is at the remote unit's timeslot. The remote unit's time slot is with respect to when the remoteunit receives the spread-spectrum-time-multiplexed signal from the basestation, and decodes the synchronization-code signal. A time slot for aparticular remote unit may be fixed, or variable. For a variable timeslot, a protocol signal from the base station may set the location ofthe time slot.

The remote unit generates a control signal from the decodedsynchronization-code signal. The control signal sets the time for wheneach remote unit transmits its own spread-spectrum signal. Each remoteunit has its own time slot, which is different from the time slots ofthe other remote units, for transmitting a spread-spectrum signal. Thetime slots may be set by the base station by a protocol when a remoteunit initiates communication with the base station. Asynchronization-code signal is not received, however, at the basestation. The timing for defining a frame of a received plurality ofspread-spectrum signals from the plurality of remote units is providedat the base station by the synchronization-code generator 81.

The despreader circuitry 110 despreads the receivedspread-spectrum-time-division signal as a time-division signal. Thetime-division signal is defined herein to include a plurality ofremote-privacy-encoded data signals, or a plurality of remote-datasignals, which are in different time slots based on the time when eachremote unit sent the spread-spectrum signal having the remote-datasignal or the remote-privacy-encoded data signal. The despreadercircuitry removes the chip-code signal which was added to thespread-spectrum signal by each of the plurality of remote units. If eachof the plurality of remote units uses the same chip codeword, then onlyone despreader circuitry is required. The plurality of remote units maybe divided into two or more sets of remote units, with each set using itown chip codeword. For each of the chip codewords the despreadercircuitry would include corresponding devices, connected in parallel,for despreading each of the corresponding set of spread-spectrumsignals. Although some of the spread-spectrum signals would be receivedwith a different spreading sequence, they are still receivedsequentially in time from the plurality of remote units. Thus, atime-division signal, as defined herein, would be outputted form thedespreader circuitry.

The received time-division signal is demultiplexed by the demultiplexer115 as a plurality of remote-privacy-encoded data signals, or aplurality of remote-data signals if the spread-spectrum signals sent bythe plurality of remote units were not privacy encoded. Essentially, theplurality of remote-privacy-encoded data signals were transmitted by aremote unit, and each remote-privacy-encoded data signal is decoded bydecoder circuitry which, for a particular remote-privacy-encoded-datasignal, includes the privacy-code generator 121 and EXCLUSIVE-OR gate122.

The synchronization-code generator 81, which is the same as used by thespread-spectrum transmitter of FIG. 1, generates thesynchronization-code signal which triggers the timing andsynchronization circuit 120 to generate a timing signal for clocking thedemultiplexer 115. The timing signal also triggers the privacy-codedgenerator 121 so that the remote-privacy-encoded signal from thedemultiplexer 115 is decoded at the appropriate time.

The present invention also includes a plurality of remote units, witheach remote unit receiving the spread-spectrum-time-multiplexed signalwhich is transmitted from the base station. Thespread-spectrum-time-multiplexed signal has a synchronization-codesignal and the plurality of privacy-encoded data signals, at the firstcarrier frequency. Within the plurality of privacy-encoded data signalsis a particular privacy-encoded data signal, defined herein as a firstprivacy-encoded data signal, to be received by the remote unit. Theremote unit also spread-spectrum transmits a remote-data signal at asecond carrier frequency. Generally, the remote unit includesremote-despreader means, remote-synchronization means, control means,remote-decoder means, remote-privacy means, remote-spreading means, andremote-transmitter means.

As illustratively shown in FIG. 3, an antenna 198 is coupled through atransmit-receive switch 199 to a bandpass filter 151. The bandpassfilter 151 is coupled to a mixer 152, which is also coupled to thesecond oscillator 153. The mixer 152 is coupled to anautomatic-gain-control (AGC) circuit 154.

The remote-despreader means is embodied as despreader circuitry 155, theremote-synchronization means is embodied as synchronization-code matchedfilter 157, control means is embodied as the controller 161. Theremote-decoder means is shown as buffer 156, privacy-code generator 159,and EXCLUSIVE-OR gate 158. Also illustrated is a digital-to-analogconverter 160.

The spread-spectrum transmitter for the remote unit includesremote-privacy means, remote-spreading means, and remote-transmittermeans. The remote-privacy means is embodied as a privacy-code generator132, an EXCLUSIVE-OR gate 133 and buffer 134. The remote-spreading meansis embodied as the chip-code generator 165, an EXCLUSIVE-OR gate 135,and lowpass filter 136. The remote-transmitter means is embodied as anoscillator 137, product device 138, optionally anautomatic-power-control (APC) circuit 139, and a second product device 4coupled to the oscillator 153. The remote-transmitter means also mayinclude a power amplifier 141 which is coupled through thetransmit-receive switch 199 to the antenna 198.

The clock 162 provides appropriate timing synchronization for operationof the spread-spectrum transmitter and receiver of the remote unit. Theclock signals are time-divided by first remote divider 163 and secondremote divider 164. For the embodiment of FIG. 3, by way of example, thefirst remote-divider 163 divides the timing of the clock signal by 15,and the second remote divider 164 divides the timing of the signal fromthe first remote divider 163 by 100. The timing signals from the seconddivider 164 provide appropriate timing for the privacy-code generator132, and analog-to-digital converter 131. The output of the firstdivider 163 provides timing for the buffer 134.

A received spread-spectrum-time-multiplexed signal at antenna 198 passesthrough the transmit-receive switch 199 and is filtered by bandpassfilter 151. The mixer 152, in cooperation with the oscillator 153,shifts the received spread-spectrum-time-multiplexed signal to anappropriate intermediate frequency or baseband frequency for processingby despreader circuitry 155. The appropriate intermediate frequency orbaseband frequency is determined on the particular embodiment ofdespreader circuitry 155. The AGC circuit 154 normalizes the power ofthe received spread-spectrum-time-multiplexed signal.

The despreader circuitry 155 may be embodied as a surface-acoustic-wavedevice, a tapped-delay-line match filter, or a correlator or any othercircuitry which may be used for despreading the receivedspread-spectrum-time-multiplexed signal, as is well known in the art. Asillustratively shown in FIG. 4, the correlator may include a chip-codegenerator 415, a mixer 410 and a filter 420. The despread,spread-spectrum-time-multiplexed signal is the time-multiplexed signal,which was originally sent by the spread-spectrum transmitter at the basestation.

The synchronization-code matched filter 157 detects thesynchronization-code signal embedded in the time-multiplexed signal, andsends an appropriate timing signal to the controller 161. In response tothe timing signal from the synchronization-code-matched filter 157, thecontroller 161 generates appropriate control signals which actuatebuffer 156, privacy-code generator 159 and digital-to-analog converter160, so that the appropriate channel from the time-multiplexed signal isdemultiplexed and received at the remote unit. As an example, thesynchronization-code-matched filter 157 may be embodied as a 160 bitstage matched filter, which is matched to a 160 bit codeword used togenerate the synchronization-code signal. The buffer 156 stores only theselected privacy-encoded data signal, or the selected data signal, andnot the entire time-multiplexed signal. The selected privacy-encodeddata signal, or the selected data signal, is the signal which is desiredto be received at the remote unit. When receiving the selected firstprivacy-encoded data signal, the privacy-code generator 159 generates afirst privacy-coded signal which is processed by the EXCLUSIVE-OR gate158 to generate the first data signal. In a preferred embodiment, analogvoice may be converted to a data signal and transmitted to a remoteunit. In this embodiment, the digital-to-analog converter 16 convertsthe first data signal to the analog voice signal as an output signal.

If the analog voice were to be transmitted from the remote unit to abase station, then the analog signal input would be converted byanalog-to-digital converter 131 to a remote-data signal, d_(Hi) (t).When privacy is used, the remote-data signal is encoded with aremote-privacy-code signal by the EXCLUSIVE-OR gate 133 as aremote-privacy-encoded-data signal. The remote-privacy-code-signal isgenerated by the privacy-coded generator 132. The remote-privacy-encodeddata signal is stored in the buffer 134. With an appropriate timing fromthe first divider 163, the remote-privacy-encoded data signal isspread-spectrum processed by EXCLUSIVE-OR gate 135 with a secondchip-code signal generated by the chip-code generator 165 using theappropriate chip codeword assigned to the remote unit. The lowpassfilter 136 filters the spread-spectrum signal. The spread-spectrumsignal is shifted to a second carrier frequency by operation of firstmixer 138 and oscillator 137, and second mixer 140 and oscillator 153.The APC circuit 139 regulates the power transmitted by the remotestation in response to a level provided by AGC circuit 154. Thespread-spectrum signal is amplified by power amplifier 141 and radiatedby antenna 198.

The controller 161 provides the control signal to the transmit-receiveswitch 199 so that upon receiving and decoding the synchronization-codesignal, and thereby generating the control signal, the transmit-receiveswitch 199 is directed to the power amplifier 141 for transmitting thespread-spectrum signal. After transmitting the spread-spectrum signal,the transmit-receive switch 199 returns to the position for receiving aspread-spectrum-time-multiplexed signal. The transmit-receive switch 199is always on receive except during transmission.

Thus, the spread-spectrum receiver of the remote unit detects itsreceived time slot and the synchronization-code signal in thespread-spectrum-time-multiplexed signal received from the base station.

The present invention also includes, at a base station, the method forspread-spectrum processing a plurality of data signals on a firstcarrier frequency by generating a synchronization-code signal, encodingthe plurality of data signals with a plurality of privacy-code signalsas a plurality of privacy-encoded data signals, respectively,time-multiplexing the synchronization-code signal and the plurality ofprivacy-encoded data signals, respectively, to generate atime-multiplexed signal, spread-spectrum processing the time-multiplexedsignal with a chip-code signal to generate aspread-spectrum-time-multiplexed signal, and converting thespread-spectrum-time-multiplexed signal to a form suitable for sendingover the communications channel.

Also, at the base station, the method includes receiving aspread-spectrum-time-division signal by despreading thespread-spectrum-time-division as a time-division signal, demultiplexingthe time-division signal as a plurality of remote-privacy-encoded datasignals, generating a timing signal and decoding, using the timingsignal, the plurality of remote-privacy-encoded signals as a pluralityof remote-data signals.

At a remote unit, the method includes receiving aspread-spectrum-time-multiplexed signal, which has a synchronizationsignal and a first privacy-encoded-data signal, at a first carrierfrequency, and spread-spectrum transmitting a remote-data signal at asecond carrier frequency. The second carrier frequency may be the sameas the first carrier frequency. The method includes despreading thespread-spectrum-time-multiplexed signal as a time-multiplexed signal,and detecting in the time-multiplexed signal, the synchronization-codesignal. In response to detecting the synchronization-code signal, atiming signal and a control signal are generated. A firstprivacy-encoded-data signal is decoded from the time-multiplexed signalas first data signal.

The method, at the remote unit, also includes encoding a remote-datasignal with a remote-privacy-code signal as aremote-privacy-encoded-data signal. The method spread-spectrum processesthe remote-privacy-encoded-data signal with a second chip-code signal asa spread-spectrum signal, and converting the second spread-spectrumsignal to a form suitable for sending over a communications channel.

FIG. 5 illustratively shows, at the output of the multiplexer 75, thetime-multiplexed signal as a synchronization-code signal, g_(o) (t)concatenated with a plurality of privacy-encoded data signals. Theplurality of privacy-encoded-data signals are represented, by way ofexample, as 100 privacy-encoded data signals. The plurality ofprivacy-encoded-data signals alternatively may be a plurality of datasignals, if privacy encoding is not used. The first privacy-encoded datasignal 401, 99^(th) privacy-encoded data signal 499, and 100^(th)privacy-encoded data signal 500 are shown. In a particular embodiment, aparticular privacy-encoded data signal might be encoded as 160 bits, asillustratively shown in FIG. 5.

FIG. 6 illustrates the time slots 300 of the time-multiplexed signal,where the synchronization-code signal is at position zero andsubsequently followed by 100 slots for privacy-encoded data signals. Ata particular remote unit, for example a first remote unit which receivesthe first channel of the time-multiplexed signal, the remote unittransmits at a short time later a spread-spectrum signal back to thebase station. Timing is shown as slot 350 for the remote unit, and thetime slots 300 are shown for the base station.

The spread-spectrum transmitter at the base station alternatively maytransmit the plurality of data signals, or the plurality ofprivacy-encoded-data signals, at the same time, using code divisionmultiple access. A block diagram for such a base station transmitter isshown in FIG. 7 with its corresponding timing sequence illustrated inFIG. 8. An alternative block diagram for a base station transmitter isshown in FIG. 9 with its corresponding timing sequence illustrated inFIG. 10.

Accordingly, a spread-spectrum transmitter for spread-spectrumprocessing a plurality of data signals on a carrier frequency maycomprise base-synchronization means, a plurality of base-privacy means,a plurality of base-spreading means, combiner means, multiplexer means,and base-transmitter means. The plurality of base-privacy means isoptional. In FIG. 7, the base-synchronization means is embodied as asynchronization code generator 81, and the plurality of base-privacymeans is embodied as EXCLUSIVE-OR gate 51 and first privacy-codegenerator 52, EXCLUSIVE-OR gate 61 and second privacy-code generator 62,through EXCLUSIVE-OR gate 71 and N^(th) privacy-code generator 72. Thefirst privacy-code generator 51 generates a first privacy-code signal,the second privacy-code generator generates a second privacy-codesignal, and the N^(th) privacy-code generator generates an N^(th)privacy code signal. EXCLUSIVE-OR gate 51 is coupled to first privacycode generator 52 and uses the first privacy-code signal for encodingthe first data signal as a first privacy-encoded-data signal.EXCLUSIVE-OR gate 61 is coupled to second privacy-code generator 62 anduses the second privacy-code signal for encoding the second data signalas a second privacy-encoded-data signal. EXCLUSIVE-OR 71 is coupled toN^(th) privacy-code generator 72 and uses the N^(th) privacy-code signalfor encoding the N^(th) data signal as an N^(th) privacy-encoded-datasignal.

The plurality of base-spreading means is shown as EXCLUSIVE-OR gate 704coupled to synchronization-code generator 81 and tosynchronization-chip-code generator 701, EXCLUSIVE-OR gate 703 coupledto first message-chip-code generator 702, EXCLUSIVE-OR gate 773 coupledto second message-chip-code generator 772, through EXCLUSIVE-OR gate 783coupled to N^(th) message-chip-code generator 782.

The synchronization-chip-code generator 81 uses a synchronization-chipcodeword for generating a synchronization-chip-code signal. EXCLUSIVE-ORgate 704 spread-spectrum processes the synchronization-code signal withthe synchronization-chip-code signal to generate a spread-spectrumprocessed-synchronization-code signal. The first message-chip-codegenerator 702 uses a first message-chip codeword for generating a firstmessage-chip-code signal. EXCLUSIVE-OR gate 703 spread-spectrumprocesses the first privacy-encoded-data signal, or the first datasignal if privacy encoding is not used, with the first chip-code signalto generate a first spread-spectrum signal. The second message-chip-codegenerator 772 uses a second message-chip codeword for generating asecond message-chip-code signal. EXCLUSIVE-OR gate 773 spread-spectrumprocesses the second privacy-encoded-data signal, or the second datasignal if privacy encoding is not used, with the secondmessage-chip-code signal to generate a second spread-spectrum signal.Similarly, the N^(th) message-chip-code generator 782 uses an N^(th)message-chip codeword for generating a N^(th) message-chip-code signal.EXCLUSIVE-OR gate 783 spread-spectrum processes the N^(th)privacy-encoded-data signal, or the N^(th) data signal if privacyencoding is not used, with the N^(th) message-chip-code signal togenerate an N^(th) spread-spectrum signal.

The spread-spectrum processing of each of the plurality ofprivacy-encoded-data signals or each of the plurality of data signals,is done with proper timing and chip rate to produce a desiredspread-spectrum processing gain. Timing for each privacy-code generatorand for each message-chip-code generator may be from a common clocksignal as illustrated in FIGS. 7 and 9.

The combiner means is shown as combiner 705. The EXCLUSIVE-OR gate 703is coupled to the EXCLUSIVE-OR gate 51 and to combiner 705. TheEXCLUSIVE-OR gate 773 is coupled to the EXCLUSIVE-OR gate 61 and to thecombiner 705. The EXCLUSIVE-OR gate 783 is coupled to the EXCLUSIVE-ORgate 71 and to the combiner 705.

In a preferred embodiment, the combiner 705 linearly combines theplurality of spread-spectrum signals from the plurality ofbase-spreading means. Nonlinear combining may equivalently work withoutserious degradation in performance, however. The combiner 705 combinesthe plurality of spread-spectrum signals as a combined-plurality ofspread-spectrum signals.

The multiplexer means is shown as multiplexer 708, first buffer 706 andsecond buffer 707. EXCLUSIVE-OR gate 704 is coupled tosynchronization-code generator 81 and through second buffer 707 to themultiplexer 708. The combiner 705 is coupled through the first buffer706 to the multiplexer 708. The multiplexer 708 time multiplexes thespread-spectrum-processed-synchronization-code signal with thecombined-plurality of spread-spectrum signals, as amultiplexed-spread-spectrum signal. The first buffer 706 stores thecombined-plurality of spread-spectrum signals until the multiplexer 708selects the first buffer 706. The second buffer 707 stores thespread-spectrum-processed-synchronization-code signal until themultiplexer 708 selects the second buffer 707.

The base transmitter means is shown as an oscillator 74, a productdevice 78, a power amplifier 79, and an antenna 98. An isolator 99 maybe inserted between the antenna 98 and the power amplifier 79 forisolating the base-station receiver from the base-station transmitter.The product device 78 may be a mixer or other device which can raise aspread spectrum signal to a carrier frequency. The product device 78 iscoupled to the oscillator 74, the multiplexer 706 and the poweramplifier 79.

The synchronization-code generator 81 generates a synchronization-codesignal. The synchronization-chip-code generator 701 generates achip-code signal, and the EXCLUSIVE-OR gate 704 spread-spectrumprocesses the synchronization-code signal with the chip-code signal togenerator a spread-spectrum-processed-synchronization-code signal.

The plurality of privacy-code generators 52, 62, 72 generate a pluralityof privacy-code signals. The plurality of EXCLUSIVE-OR gates 51, 61, 71,encode the plurality of data signals, d₁ (t), d₂ (t), . . . , d_(N),with the plurality of privacy-code signals to generate a plurality ofprivacy-encoded-data signals, respectively. Thus, by way of example, thefirst data signal, d₁ (t), is encoded with the first privacy-code signalfrom the first privacy-code generator 52 by the EXCLUSIVE-OR gate 51 asthe first privacy-encoded-data signal. The second data signal, d₂ (t),is encoded with the second privacy-code signal from the secondprivacy-code generator 62 by the EXCLUSIVE-OR gate 61 as the secondprivacy-encoded-data signal. The N^(th) data signal, d_(N), is encodedby the N^(th) privacy-code signal from the privacy-code generator 72 bythe EXCLUSIVE-OR gate 71 as the N^(th) privacy-encoded-data signal.

The plurality of EXCLUSIVE-OR gates 704, 703, 773, 783, spread spectrumprocess the synchronization-code signal and the plurality ofprivacy-encode data signals, or data signals if privacy encoding is notused, with a plurality of chip-code signals to generate a plurality ofspread-spectrum signals. The plurality of chip-code signals aregenerated by the synchronization-chip-code generator 701, firstmessage-chip-code generator 702, second message-chip-code generator 772through N^(th) message-chip-code generator 782. The plurality ofEXCLUSIVE-OR gates 704, 703, 773, 783 spread-spectrum process thesynchronization-code signal and the plurality of privacy-encoded-datasignals by modulo-2 adding the plurality of chip-code signals.Accordingly, the synchronization-code signal is modulo-2 added to thesynchronization-chip-code signal from synchronization-chip-codegenerator 701 by EXCLUSIVE-OR gate 704. The first privacy-encoded-datasignal is modulo-2 added by the EXCLUSIVE-OR gate 703 to the firstchip-code signal from the first message-chip-code generator 702. Thesecond privacy-encoded-data signal is modulo-2 added by the EXCLUSIVE-ORgate 773 to the second chip-code signal from the secondmessage-chip-code generator 772. The N^(th) privacy-encoded-data signalis modulo-2 added to the N^(th) chip-code signal from the N^(th)message-chip-code generator 782 by the EXCLUSIVE-OR gate 783.

The combiner 705 combines the plurality of spread-spectrum signals fromthe plurality of EXCLUSIVE-OR gates 703, 773, 783 to generate acombined-spread-spectrum signal. The multiplexer 706 time multiplexesthe spread-spectrum-processed-synchronization-code signal with thecombined-plurality of spread-spectrum signals.

The multiplexed-combined spread-spectrum signal is converted to a formsuitable for sending over a communications channel by function of theoscillator 74 raising the multiplexed-combined-spread-spectrum signal toa carrier frequency with product device 78. The power amplifier 79amplifies the multiplexed-combined-spread-spectrum signal at the carrierfrequency, which is radiated by antenna 98. The spread-spectrum systemtiming is shown in FIG. 8. In this case, thespread-spectrum-processed-synchronization-code signal is sent first andthen the combined-plurality of spread-spectrum signals is sent as a baseCDMA signal. Subsequently, each mobile unit sends its signal to the basestation in its selected time slot, as previously discussed.

The present invention of FIG. 7 can be modified as shown in FIG. 9 byhaving the synchronization-code signal become a generic-chip-code signalwhich is combined at the same time with the spread-spectrum signals fromthe plurality of EXCLUSIVE-OR gates 703, 773, 783. A generic-chip-codesignal is used without spread-spectrum processing a data signal, or forspread-spectrum processing a data signal with a relatively low datarate. Accordingly, a spread-spectrum channel which is despread with thegeneric-chip-code signal can be used to derive a carrier signal, whicheffectively can be used as a pilot signal. The carrier signal or pilotsignal can be used for synchronously despreading the otherspread-spectrum channels and provide other timing at a remote unitreceiver. In this case, as shown in FIG. 10, the generic-chip-codesignal is sent concurrently in time with the plurality ofspread-spectrum signals as the combined spread-spectrum signal, over thecommunication channel. Subsequently, each mobile unit sends its messageto the base station, as set forth previously, in a time slot measuredfrom the generic-chip-code code signal. Timing may be derived from acommon clock signal and/or the generic-chip-code signal.

In use, a spread-spectrum transmitter of FIG. 1 at a base stationencodes a plurality of data signals with a plurality of privacy-codesignals to generate a plurality of privacy-encoded data signals,respectively. A synchronization-code signal is generated by thesynchronization-code generator, and is time multiplexed with theplurality of privacy-encoded data signals by multiplexer 75 to generatea time-multiplexed signal. The time-multiplexed signal isspread-spectrum processed by EXCLUSIVE-OR gate 76 using a firstchip-code signal generated by a chip-code generator 56, to generate aspread-spectrum-time-multiplexed signal. Thespread-spectrum-time-multiplexed signal is transmitted on a firstcarrier frequency over a communications channel. Thesynchronization-code signal defines a frame which includes the pluralityof privacy-encoded-data signals.

At a remote unit, the spread-spectrum-time-multiplexed signal isreceived and demultiplexed using despreader circuitry 155. Asynchronization-code matched filter 157 detects the synchronization-codesignal embedded in the despread signal, and generates a timing signal.The timing signal actuates the controller 161 for generating controlsignals, which cause the buffer 156 to store the selectedprivacy-encoded data signal embedded in the time-multiplexed signal fromthe despreader circuitry 155. The privacy-code generator 159 andEXCLUSIVE-OR gate 158 decodes the privacy-encoded data signal togenerate the data signal being received from the base station.

At the remote unit, a remote-data signal, d_(Hi) (t) is encoded byEXCLUSIVE-OR gate 133 by a remote-privacy-code signal from privacy-codegenerator 132, and the resulting remote-privacy-encoded data signal isstored in buffer 134. The buffer 134 stores theremote-privacy-encoded-data signal until the control signal is sent bycontroller 161 to transmit. The remote-privacy-encoded data signal isthen spread-spectrum processed by EXCLUSIVE-OR gate 135 using a secondchip-code signal generated by chip-code generator 165. The output of theEXCLUSIVE-OR gate 135 is a spread-spectrum signal. The control signalalso actuated the transmit-receive switch 199 to the transmit position.The spread-spectrum signal is transmitted at a second carrier frequencyover the communications channel to the base station.

The controller 161 generates the control signal which actuates thetransmit-received switch 199, to be only in the transmit position whiletransmitting from the remote unit. Otherwise, the transmit-receiveswitch 199 is in the receive mode. Additionally, the remote unit has itstiming based on detection of the synchronization-code signal, andtransmits its spread-spectrum signal within a designated time slot. Thedesignated time slot can correspond to the time slot of theprivacy-encoded data signal being received by the remote unit from thebase station.

At the base station a plurality of spread-spectrum signals are receivedand despread. The plurality of spread-spectrum signals have beendesignated herein as a spread-spectrum-time-division signal, inasmuch asthe plurality of spread-spectrum signals are received sequentially intime. At the base station, each spread-spectrum signal is despread as atime-division signal. The time-division signal is demultiplexed bydemultiplexer 115 as a plurality of remote-privacy-encoded data signals.Appropriate circuitry is used to decode the remote-privacy-encoded datasignal as the remote-data signal, d_(Hi) (t).

It will be apparent to those skilled in the art that variousmodifications may be made to the CDMA/TDMA spread-spectrum system of theinstant invention without departing from the scope or spirit of theinvention, and it is intended that the present invention covermodifications and variations of the CDMA/TDMA spread-spectrum systemprovided they come within the scope of the appended claims and theirequivalents.

I claim:
 1. A spread-spectrum transmitter for spread-spectrum processinga plurality of data signals on a carrier frequency, f_(o), comprising:aplurality of privacy-code generators for generating a plurality ofprivacy-code signals, respectively; a plurality of EXCLUSIVE-OR gatescoupled to said plurality of privacy-code generators for modulo addingeach of the respective plurality of privacy-code signals to each of theplurality of data signals to generate a plurality of privacy-encodeddata signals, respectively; a plurality of data buffers coupled to saidplurality of EXCLUSIVE-OR gates for storing the plurality ofprivacy-encoded data signals, respectively; a synchronization-codegenerator for generating a synchronization-code signal; asynchronization buffer coupled to said synchronization-code generatorfor storing the synchronization-code signal; a multiplexer coupled tosaid synchronization buffer and to said plurality of data buffers fortime multiplexing the synchronization-code signal and the plurality ofprivacy-encoded-data signals, respectively, to generate atime-multiplexed signal; a chip-code generator for generating achip-code signal; an EXCLUSIVE-OR gate coupled to said multiplexer andto said chip-code generator for spread-spectrum processing thetime-multiplexed signal with the chip-code signal as aspread-spectrum-time-multiplexed signal; and a transmitter fortransmitting the spread-spectrum-time-multiplexed signal on the carrierfrequency over a communications channel.
 2. A spread-spectrumtransmitter for spread-spectrum processing a plurality of data signalson a carrier frequency, comprising:base-synchronization means forgenerating a synchronization-code signal; base-privacy means forencoding a plurality of data signals with a plurality of privacy-codesignals as a plurality of privacy-encoded-data signals, respectively;multiplexer means for time multiplexing the synchronization-code signaland the plurality of privacy-encoded-data signals, respectively, togenerate a time-multiplexed signal; base-spreading means forspread-spectrum processing the time-multiplexed signal with a chip-codesignal to generate a spread-spectrum-time-multiplexed signal; andbase-transmitter means for converting thespread-spectrum-time-multiplexed signal to a form suitable for sendingover a communications channel.
 3. The spread-spectrum transmitter as setforth in claim 2 wherein said base-privacy means includes:a plurality ofprivacy-code generators for generating the plurality of privacy-codesignals, respectively; and a plurality of EXCLUSIVE-OR gates for moduloadding each of the respective plurality of privacy-code signals to eachof the plurality of data signals, respectively.
 4. The spread-spectrumtransmitter as set forth in claim 2 wherein said multiplexer meansincludes:a plurality of data buffers for storing the plurality ofprivacy-encoded-data signals; a synchronization buffer for storing thesynchronization-code signal; and a multiplexer for time multiplexing thesynchronization-code signal and the plurality of privacy-encoded-datasignals, respectively, to generate the time-multiplexed signal.
 5. Thespread-spectrum transmitter as set forth in claim 2 wherein saidbase-spreading means includes:a chip-code generator for generating achip-code signal; and an EXCLUSIVE-OR gate for spread-spectrumprocessing the time-multiplexed signal with the chip-code signal togenerate the spread-spectrum-time-multiplexed signal.
 6. Thespread-spectrum transmitter as set forth in claim 2 wherein saidbase-transmitter means includes:an oscillator for generating a carrierfrequency; a product device for shifting thespread-spectrum-time-multiplexed signal to the carrier frequency; apower amplifier for amplifying the spread-spectrum-time-multiplexedsignal at the carrier frequency; and an antenna for radiating theamplified spread-spectrum-time-multiplexed signal at the carrierfrequency over the communications channel.
 7. A spread-spectrumtransmitter for spread-spectrum processing a plurality of data signalson a carrier frequency, comprising:synchronization means for generatinga synchronization-code signal; multiplexer means for time multiplexingthe synchronization-code signal and the plurality of data signals,respectively, to generate a time-multiplexed signal; spreading means forspread-spectrum processing the time-multiplexed signal with a chip-codesignal to generate a spread-spectrum-time-multiplexed signal; andtransmitter means for converting the spread-spectrum-time-multiplexedsignal to a form suitable for sending over a communications channel. 8.The spread-spectrum transmitter as set forth in claim 7 wherein saidmultiplexer means includes:a plurality of data buffers for storing theplurality of data signals; a synchronization buffer for storing thesynchronization-code signal; and a multiplexer for time multiplexing thesynchronization-code signal and the plurality of data signals,respectively, to generate the time-multiplexed signal.
 9. Thespread-spectrum transmitter as set forth in claim 7 wherein saidspreading means includes:a chip-code generator for generating achip-code signal; and an EXCLUSIVE-OR gate for spread-spectrumprocessing the time-multiplexed signal with the chip-code signal as thespread-spectrum-time-multiplexed signal.
 10. The spread-spectrumtransmitter as set forth in claim 7 wherein said transmitter meansincludes:an oscillator for generating a carrier frequency; a productdevice for shifting the spread-spectrum-time-multiplexed signal to thecarrier frequency; a power amplifier for amplifying thespread-spectrum-time-multiplexed signal at the carrier frequency; and anantenna for radiating the amplified spread-spectrum-time-multiplexedsignal at the carrier frequency over a communications channel.
 11. Aspread-spectrum receiver for spread-spectrum processing aspread-spectrum-time-division signal, wherein thespread-spectrum-time-division signal includes a plurality ofspread-spectrum signals received sequentially in time from a pluralityof remote units, comprising:a despreader circuit for despreading thespread-spectrum-time-division signal as a time-division signal; ademultiplexer coupled to said despreader circuit for demultiplexing thetime-division signal as a plurality of remote-privacy-encoded-datasignals; a synchronization-code generator for generating asynchronization-code signal; a timing circuit coupled to saidsynchronization-code generator and responsive to thesynchronization-code signal for generating a timing signal; a pluralityof privacy-code generators coupled to said timing circuit and responsiveto the timing signal for generating a plurality of remote-privacy-codesignals; and a plurality of EXCLUSIVE-OR gates coupled to saiddemultiplexer and to said plurality of privacy-code generators fordecoding the plurality of remote-privacy-encoded-data signals,respectively, as a plurality of remote-data signals.
 12. Thespread-spectrum receiver as set forth in claim 11 wherein saiddespreader means includes a surface-acoustic-wave device for despreadingthe received spread-spectrum-time-division signal as the time-divisionsignal.
 13. The spread-spectrum receiver as set forth in claim 11wherein said despreader means includes a tapped-delay-line matchedfilter for despreading the received spread-spectrum-time-division signalas the time-division signal.
 14. The spread-spectrum receiver as setforth in claim 11 wherein said despreader means includes:a chip-codegenerator for generating a chip-code signal; a mixer coupled to saidchip-code generator and responsive to the chip-code signal fordespreading the received spread-spectrum-time-division signal as thetime-division signal; and a filter coupled to said mixer for filteringthe time-division signal.
 15. A spread-spectrum receiver forspread-spectrum processing a spread-spectrum-time-division signal,wherein the spread-spectrum-time-division signal includes a plurality ofspread-spectrum signals received sequentially in time from a pluralityof remote units, comprising:despreader means for despreading thespread-spectrum-time-division signal as a time-division signal; anddemultiplexer means for demultiplexing the time-division signal as aplurality of remote-data signals.
 16. The spread-spectrum receiver asset forth in claim 15 wherein said despreader means includes asurface-acoustic-wave device for despreading the receivedspread-spectrum-time-division signal as the time-division signal. 17.The spread-spectrum receiver as set forth in claim 15 wherein saiddespreader means includes a tapped-delay-line matched filter fordespreading the received spread-spectrum-time-division signal as thetime-division signal.
 18. The spread-spectrum receiver as set forth inclaim 15 wherein said despreader means includes:a chip-code generatorfor generating a chip-code signal; a mixer coupled to said chip-codegenerator and responsive to the chip-code signal for despreading thereceived spread-spectrum-time-division signal as the time-divisionsignal; and a filter coupled to said mixer for filtering thetime-division signal.
 19. The spread-spectrum receiver as set forth inclaim 15 wherein said demultiplexer means includes a demultiplexer fordemultiplexing the time-division signal as the plurality of datasignals.
 20. A spread-spectrum receiver for spread-spectrum processing aspread-spectrum-time-division signal, wherein thespread-spectrum-time-division signal includes a plurality ofspread-spectrum signal received sequentially in time from a plurality ofremote units, comprising:base-despreader means for despreading thespread-spectrum-time-division signal as a time-division signal;base-demultiplexer means for demultiplexing the time-division signal asa plurality of remote-privacy-encoded data signals; base-synchronizationmeans for generating a timing signal; and base-decoder means responsiveto the timing signal for decoding the plurality ofremote-privacy-encoded signals as a plurality of remote-data signals,respectively.
 21. The spread-spectrum receiver as set forth in claim 20wherein said base-despreader means includes a surface-acoustic-wavedevice for despreading the received spread-spectrum-time-division signalas the time-division signal.
 22. The spread-spectrum receiver as setforth in claim 20 wherein said base-despreader means includes atapped-delay-line matched filter for despreading the receivedspread-spectrum-time-division signal as the time-division signal. 23.The spread-spectrum receiver as set forth in claim 20 wherein saidbase-despreader means includes:a chip-code generator for generating achip-code signal; a mixer coupled to said chip-code generator andresponsive to the chip-code signal for despreading the receivedspread-spectrum-time-division signal as the time-division signal; and afilter coupled to said mixer for filtering the time-division signal. 24.The spread-spectrum receiver as set forth in claim 20 wherein saidbase-demultiplexer means includes a demultiplexer for demultiplexing thetime-division signal as the plurality of privacy-encoded-data signals.25. The spread-spectrum receiver as set forth in claim 20 wherein saidbase-synchronization means includes:a synch-code generator forgenerating a synchronization code; and a timing circuit responsive tothe synchronization-code signal for generating a timing signal.
 26. Thespread-spectrum-receiver as set forth in claim 20 wherein saidbase-decoder means includes:a plurality of privacy-code generatorsresponsive to the timing signal for generating a plurality ofprivacy-code signals; and a plurality of EXCLUSIVE-OR gates for thedecoding the plurality of privacy-encoded data signals as a plurality ofdata signals, respectively.
 27. A remote unit for receiving aspread-spectrum-time-multiplexed signal, having a synchronization signaland a plurality of privacy-encoded data signals including a firstprivacy-encoded-data signal, on a first carrier frequency, f₁, and forspread-spectrum transmitting a remote-data signal on a second carrierfrequency, f₂, comprising:an antenna; a despreader circuit coupled tosaid antenna for despreading the spread-spectrum-time-multiplexed signalas a time-multiplexed signal; a synchronization-code matched filtercoupled to said despreader circuit and responsive to asynchronization-code signal embedded in the time-multiplexed signal forgenerating a timing signal; a controller coupled to saidsynchronization-code matched filter and responsive to the timing signalfor generating a control signal; a first buffer coupled to saiddespreader circuit and to said controller, said first buffer responsiveto the control signal for storing the first privacy-encoded-data signalembedded in the time-multiplexed signal; a first privacy-code generatorcoupled to said controller and responsive to the control signal forgenerating a first privacy-code signal; a first EXCLUSIVE-OR gatecoupled to said first privacy-code generator and to said first bufferfor decoding the first privacy-encoded-data signal as a first datasignal; a second privacy-code generator coupled to said controller andresponsive to the control signal for generating a remote-privacy-codesignal; a second EXCLUSIVE-OR gate coupled to said second privacy-codegenerator for encoding the remote-data signal with theremote-privacy-code signal as a remote-privacy-encoded-data signal; asecond buffer for storing the remote-privacy-encoded-data signal; asecond chip-code generator for generating a second chip-code signal; athird EXCLUSIVE-OR gate coupled to said second buffer and to said secondchip-code generator for spread-spectrum processing theremote-privacy-encoded signal with the second chip-code signal as aspread-spectrum signal; a transmitter for transmitting thespread-spectrum encoded signal on the second carrier frequency, f₂ ; anda transmit-receive switch responsive to the control signal for switchingthe antenna from the despreader circuit to the transmitter.
 28. Theremote unit as set forth in claim 27 wherein said despreader circuitincludes a surface-acoustic-wave device for despreading the receivedspread-spectrum-time-multiplexed signal as the time-multiplexed signal.29. The remote unit as set forth in claim 27 wherein said despreadercircuit includes a tapped-delay-live matched filter for despreading thereceived spread-spectrum-time-multiplexed signal.
 30. The remote unit asset forth in claim 27 wherein said despreader circuit includes:a firstchip-code signal; a mixer coupled to said first chip-code generator andresponsive to the first chip-code signal for despreading the receivedspread-spectrum-time-multiplexed signal as the time-multiplexed signal;and a filter for filtering the time-multiplexed signal.
 31. A remoteunit for receiving a spread-spectrum-time-multiplexed signal, having asynchronization-code signal and a plurality of privacy-encoded datasignals including a first privacy-encoded data signal, at a firstcarrier frequency, and for spread-spectrum transmitting a remote-datasignal at a second carrier frequency, comprising:remote-despreader meansfor despreading the spread-spectrum-time-multiplexed signal as atime-multiplexed signal; remote-synchronization means responsive to thetime-multiplexed signal for detecting the synchronization-code signaland generating a timing signal; control means responsive to the timingsignal for generating a control signal; remote-decoder means responsiveto the control signal for decoding the first privacy-encoded data signalembedded in the time-multiplexed signal as a first data signal;remote-privacy means responsive to the control signal for encoding theremote-data signal with a remote-privacy-code signal as aremote-privacy-encoded data signal; remote-spreading means forspread-spectrum processing the remote-privacy-encoded data signal with asecond chip-code signal to generate a spread-spectrum signal; andremote-transmitter means for converting the spread-spectrum signal to aform suitable for sending over a communications channel.
 32. The remoteunit as set forth in claim 31 wherein said remote-despreader meansincludes a surface-acoustic-wave device for despreading thespread-spectrum-time-multiplexed signal as the time-multiplexed signal.33. The remote unit as set forth in claim 31 wherein saidremote-despreader means includes a tapped-delay-time matched filter fordespreading the spread-spectrum-time-multiplexed signal as thetime-multiplexed signal.
 34. The remote unit as set forth in claim 31wherein said remote-despreader means includes:a first chip-code signal;a mixer coupled to said first chip-code generator and responsive to thefirst chip-code signal for despreading the receivedspread-spectrum-time-multiplexed signal as the time-multiplexed signal;and a filter for filtering the time-multiplexed signal.
 35. The remoteunit as set forth in claim 31 wherein:said remote-synchronization meansincludes a synchronization-matched filter responsive to thesynchronization-code signal for generating the timing signal; and saidcontrol means includes a controller responsive to the timing signal forgenerating the control signal.
 36. The remote unit as set forth in claim31 wherein said remote-decoder means includes:a first buffer responsiveto the control signal for storing the first privacy-encoded data signalembedded in the time-multiplexed signal; a first-privacy-code generatorresponsive to the control signal for generating a privacy-code signal;and a first EXCLUSIVE-OR gate for decoding the first privacy-encodeddata signal as the first data signal.
 37. The remote unit as set forthin claim 31 wherein said remote-privacy means includes:a secondprivacy-code generator responsive to the control signal for generatingthe remote-privacy-code signal; and a second EXCLUSIVE-OR gate forencoding the remote-data signal with the remote-privacy-code signal asthe remote-privacy-encoded data signal.
 38. The remote unit as set forthin claim 31 wherein said remote-spreading means includes:a second bufferfor storing the remote-privacy-encoded data signal; a second chip-codegenerator for generating a second chip-code signal; and a thirdEXCLUSIVE-OR gate for spread-spectrum processing the secondprivacy-encoded signal with the second chip-code signal as aspread-spectrum signal.
 39. The remote unit as set forth in claim 31further including:an antenna; and a transmit-receive switch responsiveto the control signal for switching the antenna from said despreadermeans to said transmitter means.
 40. A remote unit for receiving aspread-spectrum-time-multiplexed signal, having a synchronization-codesignal and a plurality of data signals including a first data signal, ata first carrier frequency, and for spread-spectrum transmitting aremote-data signal at a second carrier frequency,comprising:remote-despreader means for despreading thespread-spectrum-time-multiplexed signal as a time-multiplexed signal;remote-synchronization means responsive to the time-multiplexed signalfor detecting the synchronization-code signal and generating a controlsignal; remote-spreading means for spread-spectrum processing theremote-data signal with a second chip-code signal as a spread-spectrumsignal; and remote-transmitter means for converting the spread-spectrumsignal to a form suitable for sending over a communications channel. 41.The remote unit as set forth in claim 40 wherein said remote-despreadermeans includes a surface-acoustic-wave device for despreading thespread-spectrum-time-multiplexed signal as the time-multiplexed signal.42. The remote unit as set forth in claim 40 wherein saidremote-despreader means includes a tapped-delay-time matched filter fordespreading the spread-spectrum-time-multiplexed signal as thetime-multiplexed signal.
 43. The remote unit as set forth in claim 40wherein said remote-despreader means includes:a first chip-code signal;a mixer coupled to said first chip-code generator and responsive to thefirst chip-code signal for despreading the receivedspread-spectrum-time-multiplexed signal as the time-multiplexed signal;and a filter for filtering the time-multiplexed signal.
 44. The remoteunit as set forth in claim 40 wherein:said remote-synchronization meansincludes a synchronization-matched filter responsive to thesynchronization-code signal for generating and timing signal; andfurther including control timing signal for generating the controlsignal.
 45. The remote unit as set forth in claim 40 wherein saidremote-spreading means includes:a second buffer for storing theremote-data signal; a second chip-code generator for generating a secondchip-code signal; and a third EXCLUSIVE-OR gate for spread-spectrumprocessing the remote-data signal with the second chip-code signal togenerate a spread-spectrum signal.
 46. The remote unit as set forth inclaim 40 further including:an antenna; and a transmit-receive switchresponsive to the control signal for switching the antenna from saiddespreader means to said transmitter means.
 47. A method forspread-spectrum processing a plurality of data signals on a carrierfrequency, comprising the steps of:generating a synchronization-codesignal; encoding a plurality of data signals with a plurality ofprivacy-code signals as a plurality of privacy-encoded data signals,respectively; time multiplexing the synchronization-code signal and theplurality of privacy-encoded data signals, respectively, to generate atime-multiplexed signal; spread-spectrum processing the time-multiplexedsignal with a chip-code signal to generate aspread-spectrum-time-multiplexed signal; and converting thespread-spectrum-time-multiplexed signal to a form suitable for sendingover a communications channel.
 48. A method for spread-spectrumprocessing a plurality of data signals on a carrier frequency,comprising the steps of:generating a synchronization-code signal;time-multiplexing the synchronization-code signal and the plurality ofdata signals, respectively, to generate a time-multiplexed signal;spread-spectrum processing the time-multiplexed signal with a chip-codesignal to generate a spread-spectrum-time-multiplexed signal; andconverting the spread-spectrum-time-multiplexed signal to a formsuitable for sending over a communications channel.
 49. A method forreceiving a spread-spectrum-time-multiplexed signal, comprising thesteps of:despreading the spread-spectrum-time-multiplexed signal as atime-multiplexed signal; and demultiplexing the time-multiplexed signalas a plurality of data signals.
 50. A method for receiving aspread-spectrum-time-division signal, comprising the stepsof:despreading the spread-spectrum-time-division signal as time-divisionsignal; demultiplexing the time-division signal as a plurality ofremote-privacy-encoded remote-data signal; generating a timing signal;and decoding in response to the timing signal, the plurality ofremote-privacy-encoded data signals as a plurality of remote-datasignals.
 51. A method of receiving a spread-spectrum-time-multiplexedsignal, having a synchronization signal and a first privacy-encoded datasignal, at a first carrier frequency, and for a spread-spectrumtransmitting a remote-data signal at a second carrier frequency, thesteps of:despreading the spread-spectrum-time-multiplexed signal as atime-multiplexed signal; detecting, in the time-multiplexed signal, thesynchronization-code signal and generating a timing signal; generating,in response to the timing signal, a control signal; decoding a firstprivacy-encoded data signal embedded in the time-multiplexed signal as afirst data signal; encoding, in response to the control signal, theremote-data signal with a remote-privacy-code signal as aremote-privacy-encoded data signal; spread-spectrum processing theremote privacy-encoded data signal with a second chip-code signal as aspread-spectrum signal; and converting the spread-spectrum signal to aform suitable for sending over a communications channel.
 52. Aspread-spectrum transmitter for spread-spectrum processing a pluralityof data signals on a carrier frequency, comprising:base-synchronizationmeans for generating a synchronization-code signal a plurality ofbase-spreading means for spread-spectrum processing thesynchronization-code signal and the plurality of data signals and with aplurality of chip-code signals to generate aspread-spectrum-processed-synchronization-code signal and a plurality ofspread-spectrum signals, respectively; combiner means for combining theplurality of spread-spectrum signals, respectively, to generate acombined-spread-spectrum signal; multiplexer means for time multiplexingthe spread-spectrum-processed-synchronization-code signal and thecombined-spread-spectrum signal as a multiplexed-spread-spectrum signal;and base-transmitter means for converting the time-multiplexedspread-spectrum signal to a form suitable for sending over acommunications channel.
 53. The spread-spectrum transmitter as set forthin claim 2, further including:a plurality of base-privacy means forencoding the plurality of data signals with a plurality of privacy-codesignals as a plurality of privacy-encoded-data signals, respectively;and wherein said plurality of base-spreading means spread-spectrumprocesses the plurality of privacy-encoded-data signals with theplurality of chip-code signals to generate the plurality ofspread-spectrum signals, respectively.
 54. The spread-spectrumtransmitter as set forth in claim 53 wherein each of said base-privacymeans includes:a privacy-code generator for generating the privacy-codesignal; and an EXCLUSIVE-OR gate for modulo-2 adding the respectiveprivacy-code signal to the data signal, respectively.
 55. Thespread-spectrum transmitter as set forth in claim 52 wherein each ofsaid base-spreading means includes:a chip-code generator for generatinga chip-code signal; and an EXCLUSIVE-OR gate for spread-spectrumprocessing the privacy-encoded-data signal with the chip-code signal togenerate the spread-spectrum signal.
 56. The spread-spectrum transmitteras set forth in claim 52 wherein said multiplexer means includes:a firstdata buffer for storing the combined-spread-spectrum signal; a secondbuffer for storing the spread-spectrum-processed-synchronization-codesignal; and a multiplexer for time multiplexing thespread-spectrum-processed-synchronization-code signal and thecombined-spread-spectrum signal, respectively, to generate themultiplexed-spread-spectrum signal.
 57. The spread-spectrum transmitteras set forth in claim 52 wherein said base-transmitter means includes:anoscillator for generating a carrier frequency; a product device forshifting the combined-spread-spectrum signal to the carrier frequency; apower amplifier for amplifying the multiplexed-spread-spectrum signal atthe carrier frequency; and an antenna for radiating the amplifiedmultiplexed-spread-spectrum signal at the carrier frequency over thecommunications channel.
 58. A spread-spectrum transmitter forspread-spectrum processing a plurality of data signals on a carrierfrequency, comprising:base-generic means for generating ageneric-chip-code signal; a plurality of base-spreading means forspread-spectrum processing the plurality of data signals with aplurality of chip-code signals to generate a plurality ofspread-spectrum signals; combiner means for combining thegeneric-chip-code signal and the plurality of spread-spectrum signals,respectively, to generate a combined-spread-spectrum signal; andbase-transmitter means for converting the combined-spread-spectrumsignal to a form suitable for sending over a communications channel. 59.The spread-spectrum transmitter as set forth in claim 58, furtherincluding:a plurality of base-privacy means for encoding a plurality ofdata signals with a plurality of privacy-code signals as a plurality ofprivacy-encoded-data signals, respectively; and wherein said pluralityof base-spreading means spread-spectrum processes the plurality ofprivacy-encoded-data signals with the plurality of chip-code signals togenerate the plurality of spread-spectrum signals, respectively.
 60. Thespread-spectrum transmitter as set forth in claim 59 wherein each ofsaid base-privacy means includes:a privacy-code generator for generatingthe privacy-code signal, respectively; and an EXCLUSIVE-OR gate formodulo-2 adding the respective privacy-code signal to the data signal,respectively.
 61. The spread-spectrum transmitter as set forth in claim58 wherein each of said base-spreading means includes:a chip-codegenerator for generating a respective chip-code signal; and anEXCLUSIVE-OR gate for spread-spectrum processing theprivacy-encoded-data signal with the chip-code signal to generate thespread-spectrum signal, respectively.
 62. The spread-spectrumtransmitter as set forth in claim 58 wherein each of saidbase-transmitter means includes:an oscillator for generating a carrierfrequency; a product device for shifting the combined-spread-spectrumsignal to the carrier frequency; a power amplifier for amplifying thecombined-spread-spectrum signal at the carrier frequency; and an antennafor radiating the amplified combined-spread-spectrum signal at thecarrier frequency over the communications channel.